枚举 CompareFunction

always pass.

pass if the incoming value equals the depth/stencil buffer value.

pass if the incoming value is greater than the depth/stencil buffer value.

pass if the incoming value is greater than or equal to the depth/stencil buffer value.

pass if the incoming value is less than the depth/stencil buffer value.

pass if the incoming value is less than or equal to the depth/stencil buffer value.

never pass.

pass if the incoming value is not equal to the depth/stencil buffer value.

off